The present invention relates to a typewriter ribbon cartridge or cassette assembly and, more particularly, to a switching device wherein at least one of the ribbon spools is displaceably arranged in a slot of the cartridge housing to indicate the end of the ribbon on that spool.
In conventional typewriters and similar office machines, typewriter ribbon wound on a supply spool in a cartridge passes in and out of the cartridge along a ribbon path between the supply spool and a take-up spool. The take-up spool usually has a portion thereof which is engaged by a drive mechanism on the typewriter to provide ribbon feed. In operation, it is necessary to inform the typist of the supply state of the ribbon on the spool being unwound and to indicate when the end of the supply of ribbon is reached so that the feed can be disconnected and the ribbon cartridge replaced.
British Specification No. 1,585,245, corresponding to German OS No. 2,820,266 and U.S. Ser. No. 801,286, filed May 27, 1977, describes a typewriter ribbon cartridge for typewriters which contains a feed spool having a fixed axis of rotation and a take-up spool having an axis of rotation movable along a guide path slot toward an access opening in that corresponding chamber of the typewriter ribbon housing. A viewing slot is provided so that the supply state of the ribbon on the supply spool can be readily observed. Further, it is conventional in the art of tape recorders to provide a switch device for detecting recording tape tension being threaded through the recording station in order to initiate disc connection of the recording operation when tape tension falls below a predetermined amount at the end of the tape supply.
The present invention is directed to a switching device for use with typewriter ribbon cartridges for typewriters, teleprinters, and similar office machines, which effects an accurate switching process for disconnecting the ribbon feed operation during the unwinding process at the end of the supply of ribbon.